Teletext signal processing apparatus

Abstract: A teletext signal processing apparatus for use with a display screen on which a teletext signal is displayed at a predetermined aspect ratio. The apparatus comprises a memory for storing the teletext signal. The memory is operable, on command from a control circuit, at a variable writing speed where the teletext signal is written into the memory and at a variable reading speed where the written teletext signal is read from the memory. The control circuit adjusts the reading speed with respect to the writing speed so as to display the teletext signal on the display screen at an aspect ratio specified for the teletext signal.

Description: This invention relates to a teletext signal processing apparatus for processing a teletext signal to produce an image on a display screen. Teletext has been practiced widely in Europe to display characters or the like on a television display screen and carried out on the premise that the display screen has an aspect ratio of 4:3. Although there is no problem with the use of a television employing a display screen having an aspect ratio of 4:3 specified for the teletext, the displayed image will be elongated in the horizontal direction at 4/3 (= 3/4 x 16/9) times with the use of a wide-screen type television such as a high definition television (HDTV) or the like employing a display screen having an aspect ratio of 16:9. Teletext having an aspect ratio of 16:9 may be practiced in the future. With such teletext, the displayed image will be elongated in the vertical direction. US-A-4,928,182 discloses an apparatus for displaying 4:3 aspect ratio video signals on a 16:9 display by writing them to a FIFO line store and reading out at a higher rate. It is a main object of the invention to provide a teletext signal processing apparatus for processing a teletext signal in such a manner as to produce an image having a roundness of 1 on a television display screen having an aspect ratio different from that specified for the teletext signal. There is provided, in accordance with the invention a television receiver apparatus with a wide aspect ratio display comprising: means for receiving a teletext signal; a teletext decoder for decoding the received teletext signal to produce a decoded teletext signal of narrow aspect ratio; an A/D converter for converting the decoded teletext signal; memory means for storing the A/D converted teletext signal; control means for controlling a reading speed from said memory means to be faster than a writing speed to said memory means, whereby the contents of the teletext signal which is read from the memory means are elongated in the vertical direction; a D/A converter for converting the teletext signal which is read from the memory means; switch means for selecting one of the D/A converted teletext signal and a video signal; and means for displaying an output signal of the switch means on said wide aspect ratio display. According to another aspect of the invention, there is provided a method of displaying teletext data on a wide aspect ratio display, the method comprising the steps of: receiving a teletext signal; decoding the received teletext signal to produce a decoded teletext signal of narrow aspect ratio; A/D converting the decoded teletext signal; storing the A/D converted teletext signal in a memory means; reading out the stored teletext signal at a speed faster than the speed at which it was written into the memory means whereby the contents of the teletext signal which is read from the memory means are elongated in the vertical direction; D/A converting the readout teletext signal; selecting one of the D/A converted teletext signal and a video signal; and displaying the selected signal on said wide aspect ratio display. The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Fig. 1 is a schematic block diagram showing one embodiment of a teletext signal processing apparatus made in accordance with the invention; Fig. 2 is a diagram used in explaining the relationship between the time at which teletext signal is written into the memory and the time at which the written teletext signal is read from the memory; Fig. 3A illustrates a voltage waveform showing the video signal before it is written into the memory; Fig. 3B is a diagram used in explaining an image produced on a display screen having an aspect ratio of 4:3; Fig. 3C illustrates a voltage waveform showing the video signal after it is read from the memory; Fig. 3D is a diagram used in explaining an image produced on a display screen having an aspect ratio of 4:3; Fig. 3E is a diagram used in explaining an image produced on a display screen having an aspect ratio of 16:9; and Fig. 4 is a diagram used in explaining an image produced on a display screen having an aspect ratio of 16:9. With reference to the drawings, and in particular to Fig. 1, there is shown a schematic block diagram of a teletext signal processing apparatus embodying the invention. It is now assumed that a teletext signal having an aspect ratio of 4:3 is displayed on a television employing a display screen having an aspect ratio of 16:9. The teletext signal processing apparatus includes a decoder 1 to which a coded teletext signal is fed. The decoder 1 decodes the received teletext signal into a teletext video signal. The teletext video signal is fed to an analog-to-digital converter 2 which converts it into a corresponding teletext digital signal on command from a control circuit 4. The teletext digital signal fed from the A/D converter 2 is written into a memory 3 having a capacity for storing a predetermined number (for example, two) horizontal lines of teletext video signal. The memory 3 is operable, on command from the control circuit 4, at a variable writing speed where the teletext video signal is written into the memory 3 and at a variable reading speed where the written teletext video signal is read from the memory 3. The teletext video signal read from the memory 3 is fed to a digital-to-analog converter 5 which converts it into a corresponding teletext analog signal on command from the control circuit 4. The teletext analog signal is fed from the D/A converter 5 to the first input terminal a of a change-over switch SW. The change-over switch SW has a second input terminal b to which a normal video signal is fed. The change-over switch SW selects one of the teletext video signal and the normal video signal. The selected video signal is fed to a CRT drive circuit. The control circuit 4 controls the reading speed of the memory 3 at 4/3 times of the writing speed of the memory 3. Assuming now that the frequency of the writing clock pulse signal is 4fSC where fSC is the frequency of the chroma sub-carrier signal and fSC = 4.43 MHz for PAL, the frequency of the reading clock pulse signal may be set at 16/3 x fSC. As a result, the time at which the memory 3 starts reading for each line of teletext video signal is delayed in time relative to the normal starting time, as shown in Fig. 2 where the solid lines indicate times at which the teletext signal is written into the memory 3 and the one-dotted lines indicate the times at which the written teletext signal is read from the memory 3. The operation of the teletext signal processing apparatus of the invention will be described. Fig. 3A shows the teletext video signal outputted from the decoder 1. If the teletext video signal is displayed on a display screen having an aspect ratio of 4:3, the produced image will have a roundness of 1, as shown in Fig. 3B. The teletext video signal is written into the memory 3 at a writing speed and is read from the memory 3 at a reading speed equal to 4/3 times of the writing speed. Fig. 3C shows the teletext video signal read from the memory 3. If the read teletext video signal is displayed on the display screen having an aspect ratio of 4:3, the produced image will be elongated in the vertical direction, as shown in Fig. 3D. If the read teletext video signal is displayed on a display screen having an aspect ratio of 16:9, the produced image will have a roundness of 1, as shown in Fig. 3E. In this embodiment, the time at which the teletext video signal is read from the memory 3 for each line of the teletext video signal is delayed a time interval a so that the produced image is positioned at the center of the display screen. It is to be noted, however, that the produced image may be shifted to the left or right or to one of the corners of the display screen without delaying the time at which the teletext video signal is read from the memory for each line of the teletext video signal, as shown in Fig. 4. This permits effective uses of the hatched area. For example, an operation menu or a normal video signal may be displayed on the hatched area. According to the invention, the writing and reading operation of the memory 3 is controlled in such a manner that the decoded teletext video signal is written in the memory 3 at a writing speed and the written teletext video signal is read from the memory 3 at a reading speed different from the writing speed. As a result, the teletext signal can be displayed at an aspect ratio specified for the teletext signal on the display screen. It is, therefore, possible to display an image having a roundness of 1 even though the aspect ratio specified for the teletext signal is different from the aspect ratio of the display screen. Furthermore, the teletext signal is displayed at a position shifted to the left or right or one of the corners of the display screen. This is desirable for the effective use of the blank of the display screen.

Claims: A television receiver apparatus with a wide aspect ratio display comprising: means for receiving a teletext signal; a teletext decoder (1) for decoding the received teletext signal to produce a decoded teletext signal of narrow aspect ratio; an A/D converter (2) for converting the decoded teletext signal; memory means (3) for storing the A/D converted teletext signal; control means (4) for controlling a reading speed from said memory means (3) to be faster than a writing speed to said memory means (3), whereby contents of the teletext signal which is read from the memory means are elongated in the vertical direction; a D/A converter (5) for converting the teletext signal which is read from the memory means; switch means (SW) for selecting one of the D/A converted teletext signal and a video signal; and means for displaying an output signal of the switch means on said wide aspect ratio display. A television receiver apparatus according to claim 1, wherein the timing at which the stored teletext signal is read from the memory means (3) is delayed by a predetermined time period so that the teletext signal is displayed at the centre of the wide aspect ratio display. A television receiver apparatus according to claim 1 or 2, wherein the memory means (3) has a capacity for storing a plurality of horizontal lines. A television receiver apparatus according to claim 1, 2 or 3, wherein the control means (4) also controls the operation of the A/D converter (2) and D/A converter (5). A method of displaying teletext data on a wide aspect ratio display, the method comprising the steps of: receiving a teletext signal; decoding the received teletext signal to produce a decoded teletext signal of narrow aspect ratio; A/D converting the decoded teletext signal; storing the A/D converted teletext signal in a memory means (3); reading out the stored teletext signal at a speed faster than the speed at which it was written into the memory means (3) whereby the contents of the teletext signal which is read from the memory are elongated in the vertical direction; D/A converting the readout teletext signal; selecting one of the D/A converted teletext signal and a video signal; and displaying the selected signal on said wide aspect ratio display. A method according to claim 5 wherein the stored teletext signal is read out after a delay of a predetermined time period so that the teletext signal is displayed at the centre of the wide aspect ratio display.

Inventors: USAMI MORIO, USAMI, MORIO, USAMI, MORIO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: H04N5
IPC codes: H04N5, H04N7